This invention relates to an access control facility for a service-on-demand system, comprising a set-top box which is connected to the service-on-demand system and includes a smart-card interface and a decoder which can read and decode information stored on a smart card inserted by a user into the interface, said access control facility further comprising a controller which can permit or block access to the service-on-demand system depending on the decoded information.
A service-on-demand system with such an access-control facility is described, for example, in the German journal "Funkschau", No. 3, 1996, pages 39 to 41.
Service-on-demand systems, particularly video-on-demand and pay TV, but also electronic banking and other electronically switchable value-added services, are enjoying increasing popularity.
Unlike phone cards, on which a fixed credit is stored when they are purchased, which can be gradually exhausted, so that when there is no credit left on the card, the latter will be worthless, the smart cards used in service-on-demand systems are, as a rule, replenishable against a corresponding payment or by debiting a deposit account. Frequently, however, no credit is stored on the credit card itself, but after access to the system, billing takes place via a customer-related electronic deposit account. In service-on-demand systems, therefore, it is particularly important to check the user's access authorization, which is unnecessary with phone cards.
To this end, a service-on-demand system usually comprises a plurality of set-top boxes with a smart-card interface and a decoder which reads and decodes the information stored on a smart card inserted by a user. In a controller, access to the point-to-multipoint system is then permitted or blocked depending on the decoded information. The operation of such a set-top box is described, for example, in an article entitled "Evolution of the Digital Set-Top Box", Conference Publication No. 428 of the International Broadcasting Convention, Sep. 12-16 1996, pages 277 to 282.
In differently constructed electronic environments, such as multiuser networks, unauthorized access is prevented by even further-reaching security measures. In an article by Chang and Hwang published in Computers Math. Applic., Vol. 26, No. 7, 1993, pages 19 to 27, the use of a password in addition to the use of a smart card as a prerequisite for gaining access to a computer system is described. A considerable problem arises from the transport of the password, which is entered by the user at a peripheral device, through the network to a central processing unit where authentication is performed by comparing this password with a stored list of valid passwords. On its way through the network, the password may be intercepted and deciphered, so that unauthorized persons may easily gain access to the network. Another problem is that the information stored on the smart card can be read without any evidence of the user's authority to access this information being required.